Technical Abstract:
Producers using no-till practices have observed that crop yields can greatly exceed expectations based on nutrient and water supply. For example, Ralph Holzwarth, who farms near Gettysburg, SD, has averaged 150 bu/ac of corn on his farm for the past 6 years. We were surprised with this yield, as corn yields in eastern South Dakota (Brookings County) averaged 140 bu/ac during this same time interval. One reason for our surprise is that yearly precipitation in Gettysburg is 5 inches less than in Brookings County (see Table 1). A second reason is that Ralph plants corn at 22,000 plants/ac, contrasting with a common density of 32,000 plants/ac in Brookings County. Corn fields in Gettysburg produce 7% more grain with 5 inches less water and 10,000 fewer plants per acre. An individual corn plant in Ralph’s fields produces 45% more grain than a corn plant in Brookings County.
We discussed with Ralph possible reasons for these yields that seemed out of the ordinary. Before adopting no-till, Ralph followed a winter wheat-corn-fallow rotation where corn yielded about 70 bu/ac. He noticed an immediate increase in corn yield when he started no-till practices 20 years ago, because not tilling and keeping residue on the soil surface increase water supply for crop growth. A second gain in corn yield occurred when Ralph diversified his rotations to reduce plant diseases. Crops generally yield more when grown less frequently. His rotations now include four to six crops; one typical rotation is winter wheat-corn-dry pea-corn-soybean-oat (Table 1). In contrast, producers in Brookings County grow mainly corn and soybean in a tillage-based system. Ralph also noted another jump in corn yield when he grew dry pea in front of corn. Dry pea increases corn yield by improving its resource-use-efficiency. Also, we believe that changes in the soil microbial community contribute to improved corn yield. One favorable change may be increased mycorrhizae levels. Mycorrhizae are fungi that attach to corn roots and improve crop absorption of nutrients and water in soil.
We are continuing to explore crop response to no-till systems, seeking to understand the reasons why crop yields are so favorable. Our research is examining the complex interactions among no-till, crop diversity, crop synergism, and the soil microbial community. As we gain more knowledge about these interactions, we may be able to develop cropping systems that yield more, but do not necessarily require more inputs.